524 



KNOWLEDGE 



[June 19, 1885. 



microscope on the division-plate for every line, although, as 

 a matter of fact, some of his diffraction gratings had 

 12,000 lines upon them. Where such extreme accuracy was 

 needed, he would ai-suredly adopt the most certain method, 

 which is to work with the division-plate and the micro- 

 meter-microscope. Here, indeed, is an example of perse- 

 verance. Imagine the task of adjusting the divisions 

 under the micrometer-microscope, winding-up the train of 

 wheels, lowering the diamond on the plate, startiog the 

 train, watching for a possible vibration in the mercury 

 bath during the actual ruling, which might ruin the 

 scientiiic value of the plate, then lifting the diamond by 

 the eccentric roller preparatory to recommencing the whole 

 operation — 12,000 times in succession ! 



The preparation of the diamond points has long been 

 considered as the grand secret of Xobert's success. Beyond 

 the admission of the bare fact that he did use diamonds, he 

 ke]it the secret of their preparation. When the machine 

 came into my hands I expected to be able to explain the 

 preparation of the ruling points immediately by inspection 

 with the microscope ; but the matter was far more difficult 

 than I had supposed. My appeal to diamond " experts " 

 brought me face to face with absolute contradictions. 

 There were ten diamonds with the machine. Two 

 of them were technically termed " points," pyramidal 

 fragments of diamond terminating in points. All were 

 agreed that these were untouched by the polishing mill. 

 The other eight diamonds each presented the general form 

 of two faces meeting in an " edge " ; the difficulty was to 

 decide whether the faces were in some cases (1) both 

 polished, (2) both cleaved (cleavage-faces unpolished), or 

 (3) one polished and one cleaved. The opinions of the 

 diamond experts could not be reconciled, for in two 

 instances they were wholly opposed, one party affirming 

 that both faces were polished, whilst the other party were 

 equally positive that both faces were due to cleavage alone, 

 and were not polished. Under these circumstances, it 

 appeared to me essential to submit the diamonds to a test 

 of the goniometer, with a view to determining whether 

 the angles of the natural cleavage-planes had been altered, 

 any such alteration being necessarily due to artificial 

 polishing of one or both faces. I thought it would be 

 most satisfactory to ask the assistance of a professional 

 mineralogist, and, therefore, applied to Mr. Lazarus 

 Fletcher, of the Mineralogical Department in the British 

 Museum, who very kindly undertook to examine the 

 diamonds, and measure the angles with Fuess's goniometer. 

 lu Mr. Fletcher's opinion the two " points " were untouched 

 by the polishing mill ; diamond No. 4 consisted of two 

 cleavage-faces meeting in the edge, and was untouched by 

 the mill ; in each of the seven remaining cases, one of the 

 faces meeting in the edge was an untouched cleavage-face, 

 and the other had been j)olished, and in some cases an 

 additional fact or two developed on that side. The gonio- 

 meter showed that in the polishing the angles had been 

 altered from the natural cleavage-planes by quantities 

 varying from a few minutes up to about six degrees, 

 and as no two were exactly alike, it might be assumed 

 that, as Mr. Fletcher suggested, "the alteration of the 

 angle is merely an incident of the polishing," and not 

 a condition distinctly aimed at by Herr Nobert. I 

 had previously stated (at the Royal Microscopical 

 Society) that some of the diamonds appeared to have two 

 polished faces meeting in an edge. On closer examination 

 in Mr. Fletcher's presence, I found that certain striations 

 on the faces, which I had regarded as imperfectly polished, 

 were more proliably untouched, and hence I have given my 

 adhesion unreservedly to his judgment. 



As to the mode of preparing the ruling diamonds adopted 



by Herr Nobert, I have no record, save the diamonds 

 themselves ; the matter can only be decided by conjecture. 

 After various consultations with diamond experts, I have 

 come to the conclusion that diamonds exhibiting under the 

 microscope precisely the character of the seven " edges " to 

 which I have referred, could be prepared from the frag- 

 ments of gem diamonds met with at any diamond cleaver's. 

 The cleaver would select a fragment which would admit of 

 two faces being cleaved to an edge of about 1-1 Gth or 

 l-20th inch in length ; one of these faces should be per- 

 fectly polished on the mill, as nearly as might be parallel 

 with the cleavage face ; the other face should then be cleaved 

 again parallel to its former cleavage, so as to remove the 

 edge, which would probably have been somewhat rounded 

 by the mill, thus furnishing a new and probably sharper 

 edge — a clean fractured face meeting the plane polished 

 face. The diamond should then be mounted in soft metal, 

 in a notch at the end of a piece of brass wire, by means of 

 the blowpipe. 



Nobert's original rulings appear to have been made on 

 artificially-polished surfaces. Later on, he experimented 

 with thin cover-glass, ruling on the natural or melted sur- 

 face. More recently. Dr. Schroder called his attention to a 

 kind of glass technically termed " mild " glass, and in- 

 structed him in a method of polishing, which induced him 

 to revert to artificial surfaces again. The plates ruled 

 since 1869 are probably all of "mild " glass, thinned down 

 to suit high powers. In 1869 he adopted a plan suggested 

 by Dr. Woodward-^namely, to rule on thin glass, and 

 mount the ruled plate on another thin glass, the whole 

 dropping into a countersunk opening in a brass plate three 

 by one inch, on which the data of the rulings were engraved. 

 Dr. Woodward suggested this plan in order to facilitate 

 the employment of an achromatic condenser of large 

 aperture and short focus. 



The memorandum-book shows that in ruling a 30-band 

 plate, Nobert commenced with the coarser lines, using a 

 weight-pressure of 30 grammes on the diamond, which was 

 gradually diminished until for the highest band he used 

 only 3 grammes. A later entry seems to imply that he 

 reversed the order of the ruling, commencing with the finest 

 lines and lightest pressure. 



I do not, as yet, know what means he adopted (if any) 

 to secure his rulings from the efiects of changes of tem- 

 perature on the division-plate, &c., during the process of 

 ruling. It is said that he removed from Greifswald to 

 Earth, because in the former town he found the vibration 

 detrimental ; also that his finest work was done always 

 during the night ; on these matters I have no positive in- 

 formation at present. 



In conclusion, I may express my conviction that the 

 publication of the data obtained from the examination of 

 the machine, and especially of the diamonds, will further 

 the interests of micrometry. Several ruling-machines exist 

 in Europe and America capable of dividing space as 

 minutely and accurately as Nobert's machine ; but most, 

 if not all, of them refuse to rule lines at all comparable to 

 his when the closeness exceeds about 50,000 to the inch ; 

 and this is, I believe, mainly if not wholly, due to imper- 

 fection in the diamond, or in the method of regulating its 

 pressure on the surface to be ruled. 



I venture to predict that when the history of the me- 

 chanical inventions of our time comes to be written, a large 

 measure of credit will be assigned to the mechanical genius 

 of Herr Nobert, as embodied in this ruling-machine. 



The errors of the Westminster clock during 1884 were under 

 1 sec. on 50 per cent, of the days of observation, between 1 and ^ 

 sees, on 29 per cent., between 2 and 3 sees, on 10 per cent., between 

 3 and 4 sees, on 7 per cent., and over 4 sec. on 4 per cent. 



